Christian Dannemann has been working as a professional watchmaker since January 2012, and has been a member of The British Watch & Clock Makers’ Guild since April 2015. The blog shows his attempts and failures at fixing and servicing watches.
Peter recently sent his watch in for a service and a new crystal. I’m a big fan of Rolex Submariners and this nice example from 1977 also happens to be my birth year!
It was running when it came in so it was thought that just a routine service was needed so I proceeded to disassemble the movement.
Then it came to removing the left hand threaded nut which keeps the date wheel in place. When trying to loosen the nut it just kept rotating freely but not rising up and off the post which meant that the post had to be broke.
Which indeed it was.
This is potentially a big problem, these posts are not available to purchase, so the only options are to buy an entire movement plate or to make a new post. Making a new post is of course preferable but it’s not an easy task. The post is just under 0.59mm diameter and has on the top of it a 0.5mm thread which is left handed to make it even more tricky!
Here is the nut with the snapped post stuck inside of it.
The first step is to remove the small piece of snapped post which is stuck inside of the nut, it wouldn’t turn freely out and it is too small to get a screw extractor in so it had to be milled out. First a hole is milled into some Acrylic for the nut to sit in to support it, it was made a tight push fit to keep it steady and centred. Before milling the hole to it is essential to first drill a smaller hole straight through the Acrylic. This is so the part can be pushed back out of the plastic from the other side when you’re done.
Here the end mill is cutting out the post. As the sink is cut first the zero position is set for the milling out of the post, providing the workpiece is a nice tight fit in the Acrylic.
The post is cleanly removed without any damage to the nut.
In our opinion the ability to do this kind of operation alone justifies the very reasonable cost of having one of these machines in your workshop.
The next step is to turn a post in the lathe, it is turned and then burnished to 0.585mm in diameter. The CNC machine will then be used to cut the 0.5mm left handed thread. A sink is milled into the Acrylic so that the rod is held secure, the thread cutter is then positioned in place and the thread cutting programme is run.
Here you will find several G code generating tools for anyone to use. Just enter the details into the boxes and click on generate G code. Then cut the text and paste on your computer to save and use on your CNC machine.
Here is the post and thread still attached to the rod.
The post then has to be removed from the rod so it was put back in the lathe to hold it while it was cut off with a fine saw.
The post then needs to be stoned to the correct length and with a small bevel on the end to aid fitting into the movement plate.
Here are the new and old posts next to each other.
The post is then pushed into the plate using a staking set.
The wheel and nut are fitted to check the depth of the post in the plate and to check that the end shake is correct.
And all is well, phew! The rest of the movement can now be assembled which was straight forward.
Peter also wanted a new crystal fitted but without a cyclops. I prefer the symmetry of the no date Submariner myself, but if I needed to have a watch with a date on it then I would definitely consider fitting a cyclops free crystal myself. It can easily be changed back in the future if you change your mind or decide to sell the watch.
With a brand spanking new fourth axis unit, I’m getting closer to my goal of cutting watch wheels….
This little wheel has 72 teeth, and measures 7.1mm in diameter. The tooth shape isn’t correct, as I just used a 60 degrees thread mill, but it’s just a proof of concept to show that wheels can be made on a CNC mill.
I’ve been busy with my CNC milling machine, and anything flat (minute recorder springs, setting lever springs, etc.) is no problem at all.
The final frontier are of course wheels and pinions. The fourth axis motor that came with the milling machine wasn’t very accurate, so I had to modify it in order to be usable for watch parts.
A good indicator how small you can machine is making a small pinion. The one in the photo measures 2.5mm across, and has 18 teeth, so that’s not bad for a start.
The main problem was getting a perfectly round base for the pinion, and I achieved that by milling down the round stock in the fourth axis itself, so basically using it as a lathe. The pinion end and the shaft that you can see where milled down (that’s why they aren’t that smooth), and they would get finished off in the lathe if this was a real-world part. At the moment, I’m testing the limits of my CNC milling machine, so it’s good to show what finishes you get straight out of the machine.
To see how the set-up works, here is a video of the mill in action cutting the pinion you have seen above:
Milling a 2.5mm pinion with 18 teeth - YouTube
The same thing but seen through an electronic microscope (the video is taken from the microscope screen) shows a lot better what is happening:
To make it look nicer, I finish off the pinion in the lathe.
If you know your watch parts, you might notice that the tooth shape isn’t quite right. I’ve cut the teeth with a Kyocera thread mill, so it’s a 60 degree triangle that’s cut into the wheel. The next step up will be to find wheel cutters small enough (module 0.08 – 0.05) to make proper wheels …
We’ve not been very busy posting lately, but that’s mainly because we are very busy at the workshop. Also, as you can always check out what we are working on at any moment in time, we felt that most our readers are using that feature to see what’s happening.
Today, I’m posting a more technical post, which might benefit my colleagues, rather than my clients. Anyway, it’s probably interesting to see what can be done.
Broken pivots are a regular occurrence, and on the left, you can see the two autowinder wheels from a Heuer 12 movement. The one on the left has a broken pivot.
If a part is available for reasonable amounts of money, buying a new one is always the best solution. But if the part isn’t available, or very expensive, a repair is in order.In order to fit a new pivot, the broken pivot has to be removed, and a hole has to be drilled to accommodate a new pivot. We are looking at drilling a 0.2mm (!) hole here… The tool of choice is an end mill.
This is looking very promising, and the crucial part of the operation. I have managed to drill a 0.2mm hole into the wheel, and I can now fit a new pivot into it.
Using an old 0.6mm screwdriver blade, I turn a new pivot on the lathe. It’s stepped, and has a larger diameter of 0.2mm to go into the hole of the wheel, an a stepped down 0.17mm part which is the new pivot.
Just to get an idea of size – on the left my index finger (in a nitrile glove). You cough, and the part is gone.
The new pivot fits nicely into the hole that I drilled, and just to make sure, I put a tiny drop of superglue into the hole before fitting the new pivot to make sure it stays where it’s supposed to stay.
This repair is pretty much at the limit at what you can do size-wise. I’ve got a 0.15mm end mill, so I could drill an even smaller hole, but that would definitely be the smallest I would attempt to go …
To all our readers who celebrate the season – we wish you a merry Christmas and a Happy New Year. And for our readers and customers all over the world who celebrate something else, or don’t celebrate at this time of the year, we do of course wish you our finest season’s greetings, and a Happy New Year!